The present invention relates to a belt type continuous casting machine and, more particularly, to a cooling apparatus for a steel belt type continuous casting machine which enables an improving of a flatness of a slab.
In, for example, Japanese Laid Open Application No. 100851/82, a belt mold is proposed, formed by a pair of metal belts and a pair of side fixed board disposed between these belts, with the belt mold being cooled by a flow of cooling water in a gap or water film portion defined by the metal belt and a cooling pad having a plurality of inlet ports and outlet ports, and being disposed at a back portion of the metal belt.
In accordance with the above proposed construction, the cooling water is introduced from a plurality of inlet ports provided on the cooling pad and is discharged from outlet ports disposed around the inlet ports, the cooling pad includes elongated or oblong grooves around the inlet ports on the surface thereof and the gap or water film portion is formed between the metal belt and cooling pad. The gap or water film portion functions as a bearing by supporting the external load which is represented by the static pressure of the molten steel applied to the belt mold, whereby the steel belt and the cooling pad are maintained out of contact so as to minimize if not prevent wear of the belt caused by frictional sliding.
Since the above proposed cooling pad has been developed by placing importance on its function as a bearing, such proposed cooling pad is inadequate from a viewpoint of a cooling function for restricting a rise in temperature caused by heat from the molten steel inside of the belt mold.
Generally, the cooling strength through the belt is evaluated by a heat transfer rate .alpha..sub.w, and a relationship between the flow velocity V.sub.w, and a thickness of the water film in accordance with the following relationship: ##EQU1## where: C.sub.1 is a constant.
If the formula (1) is represented by using the flow rate Q per unit of width for the belt wherein Q=V.sub.w .multidot..delta., the following relationship may be obtained: ##EQU2##
As evident from the above relationships, the cooling strength .alpha..sub.w is directly proportional to the flow velocity V.sub.w and inversely proportional to the water film thickness .delta. if the supply flow rate is constant. The lower limit of the water film thickness .delta. is set at 0.5 mm taking into consideration a rise in temperature of the cooling water itself.
For this reason, in the above-proposed cooling pad construction, in the steady state of casting, a difference arises between the cooling strength in the water flow portion formed in the elongated or oblong groove portion and in the water flow portion formed between the belt and the cooling pad except for the elongated or oblong groove portion. The difference in cooling strength causes the belt to undulate and, if the belt mold is not flat, in the steel melting state at the initial stage of pouring the molten steel, the tightness between the metal belts and fixed side boards disposed between the metal belts is seriously impaired thereby leading to a leakage of the molten steel and also to casting accidents as well as deformation of the cast slabs. At the stage in which solidification progresses, an unflat belt mold disadvantageously promotes deterioration in quality because it is impossible to obtain a flat slab surface.
The aim underlying the present invention essential resides in providing a cooling belt apparatus for a belt type continuous casting machine wherein an arrangement is provided for enabling a maintaining of at least one of a cooling effect and supporting effect to an external load substantially equal over an entire surface of the belt mold.
In accordance with advantageous features of the present invention, the deformation of the belt mold is prevented in order to obtain a flat cast slab with a good surface finish.
According to the present invention, a belt type continuous casting machine is provided which includes a belt mold having a pair of movable belts and side members, a cooling pad is disposed adjacent to the movable belt for forming a water film portion therebetween and includes a plurality of ports for supplying or running cooling fluid into the water film portion. At least one of the diameters of the ports and a vertical distance between the ports is varied for equally controlling a fluid pressure in the water film portion.
By virtue of the features of the present invention, it is possible to prevent the belt mold from deformation, and to obtain a flat cast slab with a good surface finish.